AWS RDS (Relational Databases) 
==============================
    RDS    
        Relational Database Service; OLTP; Manages SQL Databases (provisioning, backups, failover handling, etal); requires its own EC2 instance, e.g., 'db.t2.micro'; OPTIONAL Multi-AZ (auto-replicate across AZs), highly available, fault-tolerant deployment; OPTIONALL Read Replicas (<=5); can simulate failover by rebooting primary instance.  
        Supports most database engines: 
            Amazon Aurora (us-east), MySQL, MariaDB, PostgreSQL, Oracle, SQL Server, ... 

            Aurora     
                MySQL-compatible RDS; Enterprise Scale (db.r3.large - db.r3.8xlarge); 1/10th cost of Oracle; 5x faster than MySQL; scales in 10 GB increments; autoscales to 64TB; compute resources scales (quickly) up to 32vCPU + 244GB memory; Redundant with 2 copies across 3 availability zones (6 copies); self-healing; 2 types of replicas: Aurora Replicas (15), MySQL Read Replica (5)   
                    
        Designed for OLTP; MAX VOLUME SIZE of RDS Provisioned IOPS storage is 6 TB, and MAX provisioned IOPS is 30,000, with MySQL and Oracle database engines;    
        
        AWS RDS CLI  https://docs.aws.amazon.com/cli/latest/reference/rds/index.html

        alt: Heroku Postgres  https://www.heroku.com/postgres    

        Aurora     
            MySQL-compatible RDS; Enterprise Scale; 1/10th cost of Oracle; 5x faster than MySQL; scales in 10 GB increments; autoscales to 64TB; compute resources scales (quickly) up to 32vCPU + 244GB memory; Redundant with 2 copies across 3 availability zones (6 copies); self-healing; 2 types of replicas: Aurora Replicas (15), MySQL Read Replica (5)   

## [@ AWS RDS](https://docs.aws.amazon.com/cli/latest/reference/rds/describe-db-engine-versions.html) :: [Managed RDBMS Engine per AMI Instance](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_PostgreSQL.html#PostgreSQL.Concepts)

```bash
# Versions list
aws rds describe-db-engine-versions \
    --engine 'postgres' \
    | jq -r '.DBEngineVersions[].EngineVersion'
```
- `9.4.7, ..., 9.6.17, 10.1, ..., 11.7, ..., 12.2` (2020-06-09)


```bash
# Versions list
aws rds describe-db-engine-versions --engine postgres \
    | jq '.DBEngineVersions | .[].EngineVersion'
```
- `"9.4.7", ..., "9.6.17", "10.1", ..., "11.7", ..., "12.2"` (2020-06-09)


# LAB - 067. Launching an RDS Instance
    - MySQL / PHP / ELB / EC2 / Route53 

    > RDS > Launch database engine > Select engine > MySQL
    > Next (button) 
    > Choose use case > dev/test 
    > Specify DB details 
        DB Instance Class: db.t2.micro
        Multi-AZ Deployment: No
    > Settings 
        Free tier: check-box
        DB Instance Identifier: db1
        Master Username: (whatever)
        Master Password: (alpha-num; >= 8 char)
        Confirm Password:
        > Next (button)  
    > Configure Advanced Settings 
        Database Name: db1
        > Create database        
    > Instances > db1
        Details  
            Security groups: rds-launch-wizard (link) > link (to EC2)
                # Make db available to all in its security group, not just one IP
                Security Group > Inbound > Type: MYSQL/Aurora > Edit  
                    Source: sg-....WebDMZ (type for dropdown menu) 
                    (default is specific IP, e.g., 69.143.188.12/32)

            # NOTE separate SGs for EC2 and RDS
                - EC2 has WebDMZ SG; RDS has rds-launch-wizard SG

    > EC2 > Launch ...
        Advanced Details: 'rds.sh'
            #!/bin/bash
            yum install httpd php php-mysql -y
            yum update -y
            chkconfig httpd on
            service httpd start
            echo "<?php phpinfo();?>" > /var/www/html/index.php
            cd /var/www/html
            wget https://s3.amazonaws.com/sempernow-test-1/connect.php 
            
            # 'connect.php'; upload it to s3; set wget link above
                <?php 
                $username = "devops"; 
                $password = "12345678"; 
                $hostname = "ENDPOINT-of-RDS_DB_INSTANCE"  (db1.cqzog4iglvjq.us-east-1.rds.amazonaws.com)
                $dbname = "db1";
                //connection to the database
                $dbhandle = mysql_connect($hostname, $username, $password) or die("Unable to connect to MySQL"); 
                echo "Connected to MySQL using username - $username, password - $password, host - $hostname<br>"; 
                $selected = mysql_select_db("$dbname",$dbhandle)   or die("Unable to connect to MySQL DB - check the database name and try again."); 
                ?>
        > Next (button)
        > Tags > Name: db1-test
        > Launch

    > EC2 > Load Balancer (classic) > Attached db1-test (EC2 instance) 
        > Route53 > Created Alias Record for '8659010.xyz' w/ ELB as target endpoint

     SUCCESS!!!
        @ 8659010.xyz :: responds with the PHP Info page.

        @ 8659010.xyz/connect.php ... responds with the php-scripted echo string...
        "Connected to MySQL using username - devops, password - 12345678, host - db1.cqzog4iglvjq.us-east-1.rds.amazonaws.com"

    # IF Connection Issues "Waiting for 8659010.xyz ..."
        > VPC > (select vpc of RDS instance) 
        > Security Groups > (select, e.g., rds-launch-wizard)
            Inbound Rules > Edit
                Type: MySQL/Aurora (3306) 
                Protocol: TCP (6) 
                Source: (WebDMZ security group)